<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="lib/react.development.js"></script>
    <script src="lib/react-dom.development.js"></script>
    <script src="lib/babel.min.js"></script>
</head>
<body>
<div id="root"></div>
</body>
<script type="text/babel">
    const root = ReactDOM.createRoot(document.querySelector("#root"));
    class App extends React.Component{
        state = {
            num:1
        }
        render(){
            setInterval(()=>{
                this.setState(prevState=>({
                    num:prevState.num+1
                }))
            },1000)
            return (
                <div>
                    {this.state.num}
                </div>
            )
        }
    }
    root.render((
        <App></App>
    ))
</script>
</html>